Which of the following is a common use for the HELO command in SMTP?

The HELO command in SMTP is essential for identifying the sending server to the receiving server. When an email client or server initiates a session with another server, it sends the HELO command followed by its domain name or IP address. This serves as a way for the server to introduce itself and establish a connection, allowing the receiving server to recognize the source of the incoming email. Identifying the sending server is an important part of the SMTP protocol, as it helps in implementing email filters and ensuring that messages are sent from legitimate sources. This mechanism is fundamental for managing email communications and plays a significant role in preventing spam and spoofing.

Other options touch on processes that involve SMTP but do not accurately describe the primary function of the HELO command. For example, although the HELO command is related to initiating a message transmission, its main role is specifically about server identification. Similarly, while closing the SMTP connection is part of the overall email transaction process, that function is handled separately by commands like QUIT. Authentication of a user's identity is also not directly associated with the HELO command, as that would typically involve other methods or commands within the email protocol.